1. Field of the Invention
The present invention relates generally to chain driven vehicles and particularly relates to a racing cart having a dual derailleur transmission actuated by a pair of trigger-operated ratchet and pawl mechanisms mounted within a pair of multi-function control handles which provide steering and braking functions as well.
2. Description of Prior Developments
Dual derailleur transmission systems for foot powered vehicles are well known and have been applied, for example, to tandem bicycles as shown in U.S. Pat. Nos. 5,209,507 and 4,502,705. While these parallel chain drive systems perform adequately for their intended purposes, that is, to allow two riders to match their respective pedalling speeds, they do not adequately address the problems associated with recumbent or semi-recumbent racing carts powered by a single rider, i.e. improving the speed characteristics of the carts.
In particular, it is desirable to maintain the center of gravity of a three or four wheel racing cart as low to the ground as possible in order to provide improved cornering and maneuverability. It is also desirable to facilitate the operation of the derailleurs so as to allow simultaneous steering, braking and shifting functions with a single hand-held control assembly.
In prior dual derailleur systems, one derailleur actuator or shift lever operates in one direction, i.e. clockwise, and the other derailleur actuator operates in the opposite direction, i.e. counterclockwise, to increase or decrease the overall gear ratio between the foot pedal sprocket and the driving sprocket connected to the road wheel. In some cases, this has caused operator confusion resulting in an upshift when a downshift is intended and vice versa.
Prior derailleur systems typically have been operated with shifting assemblies attached to some portion of a bicycle frame remotely located from the handle bar hand grips. This arrangement requires temporary removal of the driver's hands from the hand grips in order to shift gears. In some cases, this can lead to a lack of steering control during turning maneuvers and is generally considered inconvenient.
Accordingly, a need exists for a dual derailleur transmission system which allows for the mounting of relatively small diameter sprockets and chains extremely close to ground level in order to lower the center of gravity of a foot powered vehicle and thereby improve its maneuverability.
Another need exists for a chain driven racing vehicle which minimizes chain slack and resists disengagement of a chain from its front sprockets.
A further need exists for a dual derailleur system which provides consistent upshifts and downshifts with a pair of hand held shift assemblies.
Still a further need exists for a dual derailleur system which is actuated by a pair of control handles, each of which provides upshifts and downshifts while allowing a rider to maintain a full grip on the steering and braking mechanisms.
Another need exists for a dual derailleur system which combines three control functions within a single hand grip, i.e. steering, braking and gear shifting.